Design consideration of UHF RFID tag for increased reading range

We investigated the design trade-off in the development of UHF-band RFID tag for increased reading range. Using the quality factors of the tag antenna and tag chip as design parameters, the effects of the quality factors on the turn-on voltage of the tag chip and the backscattered power from the tag were examined. The design equations from the analysis indicate two regions of good impedances, one for providing high turn-on voltage for the tag chip, and the other resulting in increased radar cross section (RCS) for the antenna. An optimum quality factor which provides the best compromise of the two designs is provided. Based on the analysis, an example of the tag chip and tag antenna was designed, and the reading range test in anechoic chamber resulted in a detection distance of 5.2 m for -75 dBm reader sensitivity.